The use of animal viruses as model systems for probing the complexities of molecular mechanisms has been particularly fruitful. It is generally thought that the understanding of genetic regulation in viruses will provide an insight into similar processes in eucaryotic cells. The overall objective of our research is to systematically develop our understanding of gene regulation in virus infected cells. This knowledge will be used for studying the regulation of normal cellular genes and oncogenes and for developing in-vitro systems from which activities can be purified and characterized. In the present revised application we especially intend to accomplish the followings: 1.We shall determine the functions of the carboxylic repeated domain of the largest subunit of RNA polymerase II in transcription initiation and elongation. 2.We shall determine the involvement of T-Ag, agnoprotein and RNA secondary structure in the regulation of transcription attenuation and translation in SV40. 3.We shall use in vitro transcription of HIV-1 for the analyses of trans elements involved in transcription attenuation. 4.We shall use in vitro and in vivo transcription directed by the P38 promoter of the parvovirus minute virus of mice (MVM) for the analyses of a downstream repressor element. The acquisition of knowledge by the present research will ultimately contribute to a better understanding of the more complex phenomena in mammalian cells, such as the molecular processes of differentiation, development and malignant transformation.